1. Field of the Invention
The present invention generally relates to a shift control that controls the shifting of an automatic transmission of a vehicle based on the vehicle speed and the accelerator position. More specifically, the present invention relates to a shift control for controlling the shifting of an automatic transmission when the vehicle is traveling in an inertia state (coasting).
2. Background Information
A shift control for a continuously variable transmission typically uses a conventional shift map to control the shifting of the transmission based on the accelerator position and a target input rotational speed of the transmission. When the vehicle is traveling down a declined surface, the accelerator position generally decreases and the gear ratio of the continuously variable transmission is shifted to a higher ratio. Thus, even if the accelerator position is substantially zero when the vehicle is traveling down a declined surface, the shift control acts to maintain the gear ratio at a higher value so that engine breaking does not occur.
In response to these conventional shift control technologies, a shift control has been proposed for controlling engine braking during coasting such that the vehicle decelerates in accordance with the vehicle speed, even if the vehicle speed is high, and the feeling of deceleration is expected by a driver. One example of this technology is disclosed in Japanese Laid-Open Patent Publication No. 9-112680.
In Japanese Laid-Open Patent Publication No. 9-112680, the shift control apparatus for a continuously variable transmission determines if the longitudinal acceleration of the vehicle exceeds a threshold value when the driver has released the accelerator and the accelerator position is substantially zero. The threshold value is varied in accordance with the vehicle speed. If it is determined that the longitudinal acceleration exceeds the threshold value, then the target input rotational speed of the continuously variable transmission is corrected to a larger value and shift control of the continuously variable transmission is executed such that the corrected target input rotational speed is achieved. With the technology of Japanese Laid-Open Patent Publication No. 9-112680, sufficient engine braking can be ensured even when the vehicle speed is in a high speed region, and thus, the feeling of deceleration that drivers expect can be obtained.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved automatic transmission shift control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.